Powder coating booth

ABSTRACT

A powder spray for lengthy parts includes a booth wall structure comprised primarily of doors. A moveable roof may be raised and lowered to clean powder overspray from the interior surfaces of the booth. A cleaning process may be performed with a sideways extraction mode and a downward extraction mode. The mode change occurs when a bulkhead that travels with the moveable roof blocks the inlet duct to the recovery system. The recovery system may be a cyclone system for example. The doors of the booth are hinged so that they can be positioned for spraying operations and cleaning operations. Live hinge designs are provided and hose stress relief designs are also provided. The roof may carry accumulators for pressurized air that feed cleaning nozzles as the roof descends. In addition, exhaust air may be used to assist cleaning the interior surfaces as the roof descends. All of the energy provided for cleaning and color change may be provided by accumulators.

RELATED APPLICATIONS

This application claims the benefit of States provisional patentapplication Ser. No. 60/718,379 filed on Sep. 19, 2005 for POWDERCOATING BOOTH, the entire disclosures of which are fully incorporatedherein by reference.

SUMMARY OF THE INVENTION

The invention relates generally to powder coating booths such as may beused with powder coating material application systems and processes.More particularly, the invention relates to powder coating materialapplication systems, booths and processes for elongated objects, such asfor example lengthy extrusions.

BACKGROUND OF THE INVENTION

Powder coating materials are typically applied to objects or work piecesby spray application apparatus and processes. These spray applicationapparatus and processes include electrostatic and non-electrostaticprocesses as are well known. Spray application of powder coatingmaterial often is done in a spray booth that is used to contain andrecover powder overspray. Powder overspray may be recovered from thebooth and either recycled back to the feed center for re-use orotherwise disposed of One of the more significant aspects of any powdercoating system is a powder change operation and the associated systemdown time and labor involved in such changeovers. For example, when thecolor of the applied powder needs to be changed, the entire system mustbe cleaned and purged of the just used color before the next color canbe applied. This involves the clean and purge of spray guns, feed hosesand most importantly the spray booth. Long objects such as extrusionsthat can be up to about twenty-seven feet in length or more presentunique challenges for powder application to those objects because a tallspray booth is required for adequate powder overspray containment.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a powder spray booth iscontemplated that accommodates lengthy parts, objects or work pieces. Inone embodiment, a spray booth is provided that has a plurality of doorswith one or more of the doors being hinged for movement relative to theother doors, and further wherein the doors substantially comprise thebooth wall structure. In a specific embodiment the booth includes fourhinged doors and a vertical booth height of greater than twenty feet. Inaccordance with another aspect of the invention the booth is about threetimes greater in its vertical dimension than along its lengthwisedimension (wherein lengthwise dimension refers to an axis of travel ofparts through the booth during a powder application process.)

In accordance with another aspect of the invention, a powder spray boothis contemplated that incorporates one or more gun slots that may beselectively opened and closed. In one embodiment, a gun slot cover isprovided that may be moved between a gun slot open position that may beused during a powder application process, and a gun slot closed positionthat may be used during cleaning and powder change operations. In aspecific embodiment the gun slot cover may be realized in the form of apneumatically driven flexible member that bends to open the gun slot andrelaxes to cover the gun slot.

In accordance with another aspect of the invention, a powder spray boothis contemplated in which the booth interior surfaces may be cleaned bypressurized air provided from a moveable structural member of the booth.In one embodiment, the spray booth includes a roof or ceiling structurethat directs pressurized air against the booth interior surfaces as theroof is lowered from a first or raised position used during a powderapplication process and a second or lowered position used duringcleaning and powder change. In a specific embodiment, the roof carries aplurality of pressurized air devices, such as for example nozzles thatdirect pressurized air at the booth interior surfaces. Air may beprovided to such devices for example by one or more accumulators or airtanks carried on top of the moveable roof. In another embodiment thatutilizes hinged doors as the booth wall structure, one or more of thedoors may also carry pressurized air devices for removing powder off thebooth floor.

In accordance with another aspect of the invention, a powder spray boothis contemplated that includes pressurized air devices for removingpowder overspray off the booth interior surfaces. In one embodiment, thecleaning energy used to remove powder from the interior surfaces in theform of pressurized air is sourced from one or more accumulators. In amore specific embodiment, the pressurized air source is intermittentlytriggered so that blasts of air are directed at the interior surfaces ofthe spray booth. This produces pressure waves that dislodge powderoverspray from the spray booth interior surfaces.

In accordance with another aspect of the invention, a powder spray boothis contemplated that is cleaned by a combination of pressurized airdevices and flow of exhaust air into the booth such that the exhaust airassists in removing powder from interior surfaces of the spray booth. Inone embodiment, a ceiling structure is provided that has a closelyspaced relationship to the interior surfaces of the spray booth. A gapis provided between the ceiling structure and the interior surfaces sothat exhaust air is pulled into the spray booth through the gap andapplies a shearing force against powder particles on the interiorsurfaces to dislodge them. The ceiling structure may also carrypressurized air devices that direct high volume pressurized air in theform of pressure waves at the interior surfaces. In a specificembodiment, the ceiling structure may be raised and lowered within thespray booth. The invention further contemplates the cleaning methodembodied in such apparatus, in particular a method for cleaning theinterior surfaces of a spray booth including the steps of using exhaustair flow into the booth for part of the cleaning energy andintermittently applied pressure waves.

In accordance with another aspect of the invention, a hose strain reliefmechanism is provided. The hose strain relief concept has application inany material application system that uses one or more flexible hoses. Inthe context of a spray booth for elongated parts such as described inthe exemplary embodiments herein, the hose strain relief feature isuseful due to very long and heavy hose runs particularly to the upperregions of the spray booth.

In accordance with another aspect of the invention, a cleaningarrangement and associated method for a powder spray booth iscontemplated that operates in two modes, with one mode being a sidewaysrecovery or extraction mode and the other being a downward recovery orextraction mode. In one embodiment, a spray booth is provided thatincludes a roof structure that can be raised and lowered within thebooth interior, and the booth further includes a powder recovery systemthat interfaces with the booth interior through a vertical slot andthrough a floor duct. With the roof in an upper position, powderoverspray is removed from the surfaces and drawn into the vertical slotinto the powder recovery apparatus. In one embodiment the recoveryapparatus may be a cyclone arrangement. As the roof is lowered, thepowder extraction process switches over to powder overspray beingextracted through the floor duct. In one embodiment this switch over maybe realized by providing a traveling bulkhead within a vertical recoveryduct that travels with the roof. When the roof reaches a predeterminedposition, the bulkhead blocks or isolates the recovery duct from thevertical slot and the floor duct is opened. In another embodiment, afloor slot is used adjacent to the recovery duct.

The invention further contemplates various methods embodied in the useof the described structures and or that can be carried out using suchstructures as set forth in detail hereinafter.

These and other aspects and advantages of the invention will be readilyunderstood and appreciated from the following detailed descriptionhereinafter and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective elevation of a powder spray system using severalfeatures of the present invention;

FIG. 2 is a plan view of the system of FIG. 1 with the oversprayrecovery system omitted for clarity;

FIGS. 2A, 2B and 2C illustrate the spray booth of FIG. 1 in variousexemplary but not exclusive door positions including a service position,a coating or operational position and a cleaning position respectively;

FIG. 3 is a plan view of a ceiling structure or roof in accordance withthe invention and FIG. 3A is a cross-section taken along the line 3A-3Aof FIG. 3;

FIGS. 4A and 4B are simplified illustrations of the powder recoveryducts and slots of a booth in accordance with the invention taken inelevation and perspective respectively;

FIG. 4C is an enlarged view of the intake slot portion that is circledin FIG. 4B;

FIG. 5 is a plan illustration of the spray booth of FIG. 1 showing thedoors in an open and closed position;

FIG. 6 is a detailed illustration of a live seal for a door of the spraybooth of FIG. 1;

FIG. 7 is a detailed plan illustration of a gun slot cover in accordancewith the invention;

FIGS. 8 and 9 are a perspective and an enlarged plan illustrationsrespectively of the gun slot cover and drive mechanism of FIG. 7;

FIG. 10 is a plan layout of a two booth material application system;

FIGS. 11A and 11B illustrate a hose and cable strain relief mechanismwith a gun illustrated in an extended and retracted positionrespectively;

FIG. 12 illustrates an alternative geometry for a recovery duct;

FIG. 13 is a simplified schematic of a duct blow off feature; and

FIGS. 14A and 14B illustrate additional detail of a roof structure forthe booth illustrated in FIG. 1 with the roof fully raised and nearfully raised respectively.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 illustrates a powder coating material application system 10 thatincludes a spray booth 12, a powder overspray recovery system 14, anafter filter and blower system 16, a plurality of application devices18, a gun mount and mover system 20 and an overall structural supportframework 22 (only partially illustrated in the various drawings forclarity.) The application devices 18 may be selected from any number ofspray gun designs, including a SURE-COAT™ spray gun available fromNordson Corporation, Westlake, Ohio. A feed center 21 may be providedthat contains a supply of material that will be applied to objects orwork pieces within the spray booth 12. The feed center 21 for examplemay include any number of hoppers, boxes or other containers of powder,along with suitable pumps and hoses to feed material to the applicationdevices 18. A suitable operator interface 24 to a control system (notshown) may be provided to control operation of the spray guns 18, thepowder recovery system 14, the spray booth 12 and the gun mover system20. The control system and the operator interface 24 may be selectedfrom any number of well known control system concepts as are well knownto those skilled in the art, or specifically designed for a particularsystem. The gun mover system 20 may be used to both extend and retractthe spray guns with respect to the spray booth 12 and also may be usedto produce an up down oscillatory motion of the guns during a sprayoperation.

In the exemplary embodiment, the powder overspray recovery system 14 maybe realized in the form of a cyclone system 15, however, other recoverysystem designs may be used. The blower and after filter system 16provides the energy required for operation of the cyclone recoverysystem, in the form of a substantial powder entrained exhaust air flowpulled from the spray booth interior to an intake duct of the cyclone15. The air flow produced by the recovery system also produces asubstantial flow of air into and through the spray booth 12, sometimesreferred to as containment air. The containment air flow prevents theloss of powder overspray outside the spray booth 12. In the embodimentsherein, the cyclone system 15 is a twin cyclone system, however a singlecyclone may alternatively be used. In the exemplary embodiment, powdermay either be recovered from the cyclone outlet 15 a, as is commonlydone if the powder will be reused, or alternatively may be extractedfrom the booth 12 and pass through to the after filter system 16 via abypass outlet or duct arrangement 15 b.

The cyclone 15 has a cyclone inlet 70 (FIGS. 2 and 2A) that communicateswith a first or recovery duct or plenum 74 of a vertical primary ductstructure (72, see FIG. 2). The cyclone 15 also has a bypass duct inlet76 that communicates with the bypass outlet duct 15 b and alsocommunicates with a second or bypass duct or plenum 75 that is providedin the primary duct 72. Alternatively the bypass duct 75 and therecovery duct 74 may be separate structures. The bypass arrangement mayinclude a bypass door (see below) that opens and closes depending onwhere the extracted power is to go. As will be described in greaterdetail hereinafter, a bulkhead is provided within the recovery duct 74that under certain conditions blocks the cyclone inlet 70 so that withthe bypass door open the extracted powder goes to the after filter 16via the bypass duct 75 and the bypass outlet 15 b, thus bypassing thecyclone 15.

While various concepts, aspects and features of the invention aredescribed and illustrated herein as embodied or used in combination inthe exemplary embodiments, these various concepts, aspects and featuresmay also be realized in many alternative embodiments, eitherindividually or in various combinations and sub-combinations thereof.Unless expressly excluded herein all such alternative embodiments,combinations and sub-combinations are intended to be within the scope ofthe present invention. Still further, while various alternativeembodiments as to the various aspects and features of the invention,such as alternative materials, structures, configurations, arrangements,methods, devices, software, hardware, control logic and so on may bedescribed herein, such descriptions are not intended to be a complete orexhaustive list of available alternative embodiments, whether presentlyknown or later developed. Those skilled in the art may readily adopt oneor more of the aspects, concepts or features of the invention intoadditional embodiments within the scope of the present invention even ifsuch embodiments are not expressly disclosed herein. Additionally, eventhough some features, concepts or aspects of the invention may bedescribed herein as being a preferred arrangement or method, suchdescription is not intended to suggest that such an arrangement ormethod is required or necessary unless expressly so stated. Stillfurther, exemplary or representative values and ranges may be includedto assist in understanding the present invention however, such valuesand ranges are not to be construed in a limiting sense and are intendedto be critical values or ranges only if so expressly stated.

From the approximate scale of FIG. 1 it is noted that the spray booth 12has a height or vertical dimension that is several times its length. Inone example, the spray booth 12 is about twenty-seven feet high andabout ten feet in length, wherein by ‘length’ is meant the distance thatwork pieces, parts and objects W travel through the spray booth 12 inorder to be coated with powder. Thus, the present invention contemplatesspray booths that have height to length ratios of at least about two toone and as much as about three to one or greater. This allows the spraybooth to be used for powder coating long objects such as extrusions,however, the booth may also be used for spray coating any object thatdimensionally can be accommodated through the booth. Due to the heightof the booth 12, the structural framework 22 may include platforms (notshown) that can support workers who need to maintain the spray guns 18and the gun support and mover system 20. An overhead conveyor 26(partially shown) may be used to transport parts through the boothduring a spraying operation.

While there are a number and variety of aspects and concepts to thepresent invention as set forth in greater detail herein below, two ofthese concepts should be particularly noted at the outset. The firstconcept relates to method and apparatus for cleaning the booth interiorsurfaces. The basic idea is to utilize not only the application ofpressurized air to remove powder overspray, but also to utilize energyprovided by the substantial air that is drawn into the spray booth bythe recovery system. This air flow may be thought of as the containmentair, exhaust air or a combination thereof. In accordance with theinvention, during a cleaning operation this air flow is drawn through asomewhat narrow gap adjacent the interior surfaces to create a shearforce of the air against the surfaces. This force not only removespowder overspray from the surfaces but also imparts significant kineticenergy and momentum to the dislodged particles which in turn may knockother powder particles from the interior surfaces. In conjunction withthe use of the substantial air flow into the booth via the noted gap,pressurized air may also be intermittently applied against the interiorsurfaces in the form of pressure waves. This energy also removes powderoverspray from the interior surfaces. In an exemplary embodimentdescribed below, these two cleaning concepts of using exhaust air andpressure waves are used in combination and realized by using a moveablestructure such as a roof that carries pressurized air nozzles and thatprovides the above noted gap adjacent the interior surfaces. The nozzlesare intermittently triggered to create the pressure waves, and thesource of the pressurized air in the exemplary embodiment may be one ormore storage tanks or accumulators that store a volume of pressurizedair.

The second concept to be noted is the idea of removing powder oversprayfrom the booth interior initially by a sideways extraction into avertical slot that extends along the height of the booth, wherein theslot opens to the intake of a recovery system such as a cyclone. Amoveable roof may be used to further clean interior surfaces of thespray booth, and as the roof is lowered the powder overspray extractiontransitions from a sideways extraction to a downward extraction througha duct or slot at the bottom of the booth. In the exemplary embodimentthis transition occurs by blocking or closing the cyclone intake whenthe roof reaches a predetermined position, and opening a flow passagefor powder overspray to be drawn from the booth into a bypass duct ofthe cyclone and on to the after filter system.

The spray booth 12 may be generally diamond shaped although two apexesof the diamond are somewhat truncated as will be apparent from FIG. 2which is a plan view of the basic system 10 (the after filter and blowersystem 16 being omitted for clarity, as well as the roof and some of theframe work 22.)

With reference then to FIG. 2 and FIGS. 2A-2C, the exemplary spray booth12 includes four doors 30, 32, 34 and 36 that may be hinged or otherwisemounted to the structural framework so as to be easily opened andclosed. The spray booth 12 is substantially defined by these four doors,a floor 38 and a moveable roof or ceiling structure 40. The right frontdoor 30 is hinged to one side of a gun slot panel 42 and the left frontdoor 32 is hinged to one side of a recovery duct intake panel 44. Theright rear door 36 is hinged to an opposite side of the gun slot panel42 and the left rear door 34 is hinged to an opposite side of therecovery duct panel 44. The terms front and rear are used as aconvenience to refer to the lengthwise ends of the booth that thetraveling parts enter and leave respectively it being understood thatdirection of travel through the booth may be reversed. The terms leftand right are also merely a convenience when referring to the drawings.Due to their length, the doors may be multi-piece construction having anupper section and a lower section as best illustrated in FIGS. 1 and2A-2C. Thus, other than the short (lengthwise) gun slot panel 42 thattruncates one apex of the diamond and the short (lengthwise) intakepanel 44 that truncates an opposite apex of the diamond, the booth 12has a vertical wall structure that is defined in large measure by fourhinged doors with each door comprising two (upper and lower) sections.This is in distinct contrast to prior booths that typically have a doorstructure at the booth ends but otherwise have fixed vertical walls thatdefine the booth configuration.

The hinged doors 30, 32, 34 and 36 may each be made of compositematerials including a foam core panel and gelcoat inner surface such assold by Nordson Corporation as an Apogee panel structure. Other doorstructures may alternatively be used as required. The doors may beremovably mounted using lift off hinges 46 as will be further describedherein, or other suitable hinge designs as required. The spray boothvertical wall structure is thus primarily defined by the doors.

The roof 40 may also be made of composite panels and has a generallyconforming diamond shape perimeter (generally conforming to the planshape of the booth when the doors are closed) but with a conveyor slot48 provided (FIG. 2A). The roof 40 includes an upper frame (404, FIGS.14A, 14B) that is supported by a series of cables or other suitablemechanism so that the roof can be raised and lowered in a level mannerwithin the spray booth. The roof 40 is in its uppermost position (FIG.2A) during a material application or coating operation and can belowered nearly to the floor (see FIG. 4A) during a cleaning or colorchange operation. The roof 40 is dimensioned so that the generallyconforming perimeter has a narrow lateral clearance or gap with the doorsurfaces, for example about two inches, when the doors are fully closed(FIG. 13). This narrow clearance helps to contain powder overspray whileat the same time providing a source of exhaust air drawn into andthrough the booth by the powder recovery system 14. This substantial airflow through the roof/door gaps is also used to clean the door interiorsurfaces as will be further explained.

FIG. 3 illustrates a plan view of the roof 40 panel structure. The roof40 carries a series of air nozzles 50 that may extend around the entireperiphery of the roof (in FIG. 3 not all of the nozzles are illustrated)or at least at enough intervals and positions to thoroughly clean theinterior surfaces of the doors. The roof 40 also includes a conveyorslot cover 52 that preferably is hinged so that it can be raised andlowered either manually or by operation of a suitable actuator. Thecover 52 is raised to its upright position for a spraying operation sothat the conveyor hangers can pass through the slot 48. During cleaningand/or color change operations, however, the cover 52 is lowered to itsclosed position. FIG. 3A further illustrates that the roof may includetwo air ducts 54 and 56 that extend lengthwise along either side of theconveyor slot 48 and provide an air flow down into the booth so as toprevent powder from escaping through the conveyor slot 48. As explainedbelow, the ducts 54, 56 may be coupled to a suitable source ofpressurized air.

As noted herein above, the roof 40 may include a frame structure (404,see FIG. 14) that may be supported by winch driven cables 400 so thatthe roof 40 can be raised and lowered during a cleaning operation. Sincethe roof is basically a two section structure, the closed cover 52 helpsto stabilize the roof sections as it travels up and down the booth,especially when the nozzles 50 are intermittently triggered. The roofframe 404 further supports a source or reservoir of compressed air suchas air tanks (86, FIG. 14A) or accumulators that provide high volumepressurized air to the ducts 54, 56 and the nozzles 50. The tanks 86thus provide an energy/volume storage system to deliver high volumepressurized air when the nozzles 50 are triggered, thus producing apressure wave of high volume air directed at the interior surfaces ofthe booth 12. Supply hoses are connected to the tanks 86 to replenishthem during a cleaning operation.

As best illustrated in FIGS. 2A-2C and FIGS. 4A-4B, the latter which area simplified schematic of the cyclone/booth interface, the cyclone 15interfaces with the spray booth 12 via the primary duct 72 that extendsthe height of the booth 12. The duct 72 is multi-sectional and includesan interior recovery plenum 74 that communicates with a booth intakeslot 62 formed in the intake panel 44. The plenum 74 also communicateswith the cyclone inlet 70. Powder overspray is drawn sideways into theplenum 74 from the spray booth 12 via the slot 62 and passes into thecyclone 15 via the cyclone intake duct 70. During spray coatingoperations, the roof 40 is positioned at the top of the booth 12. Theintake slot 62 extends vertically along the entire height of the booth12.

As will be further explained herein below, the floor 38 may include abypass opening 78 that may be selectively opened and closed with a slidecover 80. During a cleaning operation, as the roof 40 is lowered towardsthe cyclone inlet region, powder overspray is removed from the interiorsurfaces of the booth 12 and drawn into the intake slot 62 and into thecyclone for recovery. As the roof 40 is lowered to a point at which thecyclone inlet 70 is blocked by a bulkhead 82 (see FIG. 4A), the bypassopening 78 is opened and communicates with the vertical bypass duct 75which connects to the bypass inlet 76 above the cyclone 15 (see FIG. 4a) so that the powder entrained exhaust air bypasses the cyclone and istransported to the after filter and blower system 16. The bulkhead 82travels vertically within the recovery duct 74 at the same speed as theroof 40 during a cleaning operation. But, when the bulkhead 82 reaches aposition in which it faces and blocks off the inlet to the cyclone 15,positive stops prevent the bulkhead 82 from being lowered further eventhough the roof 40 continues to descend during a cleaning operation.When the cyclone inlet is blocked by the bulkhead 82, the bypass opening78 is opened and powder flows through the opening 80 and into the bypassrecovery duct 75 and on to the after filter and blower system 16 via thecyclone bypass duct 15 b.

The doors 30 and 36 that generally extend away from the gun slot panel42 and toward the recovery intake slot 62 may be provided with air jets(not shown) along their bottom edge so as to direct powder that falls onthe floor toward the intake slot 62 of the recovery system. Compressedair tanks or accumulators (not shown) may be disposed below the floor ofthe booth or other convenient location to supply high volume compressedair to the door air jets. In accordance with an aspect of the invention,all of the energy needed to remove overspray coating material—from thebooth interior surfaces via nozzles on the roof, the doors, gun blow offnozzles and so on—may be provided by accumulators so that the energy inthe form of high volume pressurized air can be stored and ready to use.The accumulators may be replenished during spray coating operationsalthough the accumulators 86 on the roof 40 are periodically replenishedduring a cleaning operation as will be further explained below.

The doors 30, 32, 34 and 36 are fully closed as in FIG. 2 during acleaning mode of operation. When the doors are fully closed, the doorsclosely surround the roof 40 perimeter (for example with about a lateraltwo inch gap), and the roof conveyor slot cover 52 is closed so thatpowder overspray can be removed from the interior surfaces of the boothand will be contained and not escape the booth but rather collected intothe recovery system. A gun slot cover arrangement 60 (FIG. 2 and thediscussion below referencing FIGS. 7-9) is also closed to prevent powderescaping through the gun slots 61. Prior to and/or after the conveyorslot cover 52 is closed, the roof nozzles 50 may be triggered to removepowder at the top of the booth surfaces.

The roof 40 is lowered and the air nozzles 50 that travel with the roofare used to remove powder off the interior surfaces of the doors. Inthis exemplary embodiment, the nozzles 50 are intermittently triggeredto direct pressure waves along the booth surfaces, for example about a1.5 second blast of air at about 100 psi. The accumulators 86 are sizedto permit them to be mounted on the roof frame and travel with the roof40, therefore, the accumulators 86 are not particularly large. Forexample, the accumulators 86 may be sized at about sixty gallons so thateach discharge cycle through the nozzles 50 substantially reduces thestored amount of compressed air energy in the accumulators 86. In theexemplary embodiment, it takes about eight seconds to replenish theaccumulators 86 so that the nozzles 50 are intermittently triggered orcycled at about 1.5 second on and about eight seconds off as the roof islowered. The descent rate of the roof is balanced with the replenishrate of the accumulators so that there is no loss of pressure or volumeto maintain effective cleaning of the surfaces throughout the descent ofthe roof 40.

During a cleaning as well as a coating operation, the after filtersystem 16 is constantly drawing exhaust air into the booth 12 via thecyclone 15. During a cleaning operation, this exhaust air primarilyenters the booth 12 via the gap between the roof 40 perimeter and thedoor interior 30, 32, 34, 36 surfaces throughout the descent of theroof. With reference to FIG. 4A, this high velocity air flow produces ashearing force that dislodges powder particles from the door interiorsurfaces. This shear force is the only cleaning force applied to theinterior surfaces during each eight second interval that theaccumulators 86 are being replenished. The nozzles 50 create a pressurewave that is effective for a distance of about two feet with each 1.5second trigger of high pressure air. Therefore, the rate of descent ofthe roof 40 during a cleaning operation may be selected to balance theeffective use of the nozzles 50 to blast powder from the surfaces andthe high velocity exhaust air to also dislodge powder from thesesurfaces. In one embodiment the roof may descend at about 8-10feet/minute, and the roof retracted back to the top at about 30feet/minute.

The size of the gap between the roof and the interior door surfaces maybe used to control the air flow and shear force created by the exhaustair. The after filter system 16 can draw a substantial volume of exhaustair, so the gap cannot be made so small that the head pressure on theroof creates too much strain or stress on the roof assembly. A typicalgap range may be about 1.5 inches to about 2 inches. The actual gap usedwill be determined by the booth size, the exhaust air flowcharacteristics, required cleaning time, the effectiveness of thepressure wave created periodically by the nozzles 50 and the desiredrate of descent.

The use of the exhaust air to perform a significant portion of thecleaning operation has a significant cost benefit as it allows theamount of required pressurized air to be reduced. In one embodiment, theshear forces applied by the exhaust air passing through the gap betweenthe roof and the doors provides about half of the energy needed to cleanthe booth 12 interior surfaces. This represents a substantial savings ofpressurized air that would otherwise have to be used (or other cleaningtechniques such as wiping actions).

The brief but high velocity pressure wave that is periodically appliedvia the nozzles 50 not only dislodges the powder particles from thesurfaces being cleaned, but also imparts sufficient energy to thedislodged particles that they impact other particles to dislodge them.In the exemplary embodiment herein, the pressure waves have about a twofoot effective zone so that the nozzles 50 may be intermittentlytriggered and need not produce a constant flow of pressurized air. Thepressure waves do not cause static charging or impact fusion.

The powder entrained exhaust air is drawn into the recovery system 14,such as the cyclone intake duct 70, for example, via the intake slot 62which extends vertically from the floor to the top of the booth. Sincein this example the cyclone intake duct 70 is positioned about halfwaybetween the floor 38 and the top of the booth, the intake slot 62 mayvary in width along its length, being narrower near the cyclone intakeduct 70 and wider at the top and bottom (see FIGS. 4A, 4B and 4C). Thisachieves a fairly uniform flow of air into the intake slot 62 along theentire height of the booth. For example, the intake slot 62 may be abouttwo inches at the intake duct and taper in width to about four inchesnear the top and bottom of the intake panel 44.

During a cleaning operation, which may be part of a color changeoperation for example, the doors are fully closed, the guns areretracted from the booth (powder is removed from the gun exteriorsurfaces by air nozzles positioned at the gun slots) and the gun slotcover mechanism 60 is used to close the gun slots (as will be describedhereinafter.) The conveyor slot cover 52 is also closed after allconveyor hooks have cleared the slot. The roof 40 is then lowered andpowder is removed and directed downward off the surfaces of the doorsand is drawn sideways into the intake slot 62 and the cyclone 15. Priorto lowering the roof, the nozzles 50 may be triggered.

As the roof 40 is lowered, the effective size of the booth changes. Thischanges the dynamics of the air flow into the cyclone 15. In order toefficiently continue to draw powder out of the booth interior, theoperation is changed from a sideways recovery mode via the intake slot62 to a downward or down draft recovery mode via the floor duct 78 (seeFIGS. 4A and 4B). This changeover is accomplished by providing arecovery duct bulkhead 82 that travels within the plenum 74. Thebulkhead 82 travels at about the same rate as the roof 40 while the roofis being lowered. The bulkhead 82 in one embodiment is a closed box-likestructure or frame that generally conforms to the interior shape of therecovery duct plenum 74. Any suitable means may be used to move thebulkhead such as cables for example. As the bulkhead 82 reaches theintake inlet duct 70 of the cyclone 15, it blocks the inlet to thecyclone 15. Mechanical stops 84 may be provided inside the plenum 74 tolimit further lowering of the bulkhead 82 within the plenum 74. When theinlet 70 to the cyclone is thus blocked, the floor bypass duct 78 isopened by sliding the cover 80. This allows powder that is directed downtowards the floor 38 to be exhausted from the booth through the floor,into the bypass duct 75 and into the bypass inlet duct 76 of the cyclone(sometimes referred to as a banjo) to the after filter and blower system16. After the roof has been lowered to or near the floor, it is thenraised back up to the top of the booth and the bulkhead 82 also returnsto the top of the plenum 74.

In an alternative embodiment illustrated in FIGS. 4A and 4B, in place ofthe floor opening 78, or in combination therewith, a slot 79 may beprovided between the bottom of the primary duct 72 and the floor 38.This slot 79 communicates with the recovery duct plenum 74 so thatdownward moving exhaust air and powder enters the plenum 74 via the slot79. Since the slot 79 will always be open, the exhaust air with powdermay also be selectively recovered through the bypass duct 75 into thebypass inlet 76 of the cyclone 15. For example, when the roof 40 andbulkhead 82 are still in the upper portion of the booth 12, the slot 79will communicate with the cyclone inlet 70 via the recovery duct 74.However, when the inlet 70 is blocked, the bypass duct door 81 may beopened so that the powder entrained exhaust air flows into the bypassduct 75, into the bypass outlet 15 b and on to the after filter system16. The door 81 may be realized in any convenient manner such as asimple plate valve the closes and opens the bypass outlet. A pneumaticcylinder or other motive means, including manual operation, may be usedto open and close the cyclone bypass.

The roof 40 may carry with it one or more accumulators 86 that containpressurized air and provide the energy and air needed for the airnozzles 50 that are mounted on the roof as well as the conveyor slot airplenums 54, 56. Separate accumulators may also be used to provide thepressurized air for the air jets mounted on the bottom edges of thedoors as well as the blow off nozzles for the spray guns 18. In thismanner all energy needed to clean the booth interior surfaces isprovided from accumulators so that shop air need not always be appliedto the cleaning apparatuses. The accumulators can be replenished duringa coating or cleaning operation. This allows the cleaning energy to bemaintained at a constant pressure as it is being discharged through thevarious cleaning nozzles including but not limited to the nozzles 50 onthe roof 40. The various cleaning nozzles for the guns, the floor andthe roof nozzles may be intermittently triggered at appropriateintervals such as every second and a half for example as describedabove.

FIG. 5 illustrates schematically the door positions for cleaning andspraying operations (the doors in the closed position for cleaning areshown in solid line). During cleaning the doors are fully closed. Duringspraying, the doors may be opened to any convenient dimension tomaintain adequate flow of containment air to contain the powderoverspray. In one embodiment the doors are opened to an eighteen inchgap. The doors may be opened and closed with any suitable actuatormechanism. In the embodiment of FIG. 2, pneumatic cylinders 90 and 92are used to open and close the left side doors and pneumatic cylinderdriven arms 94, 96 are used to open and close the right side doors.Proximity sensors (not shown) or other suitable position monitors may beused to control positioning of the doors. For larger booths in which thedoors include two or more sections, each section may have its ownpneumatic drive member as illustrated in FIG. 2A. A door for examplehaving an upper section 32 a and a lower section 32 b will have twoactuators 90 a and 90 b that can be operated together to move the twosections as a single door unit. Similarly, the front right side doors 30a and 30 b may be moved by actuators 96 a and 96 b.

FIG. 6 illustrates an example of a lift off hinge 46 that may be used tomount the doors but other hinge designs may be used as required. In thisexample, the hinge 46 is realized in the form of a structural steel liftoff hinge that includes a pivot pin 100. One plate 102 of the hinge ismounted to a door while the other hinge plate 104 is mounted on asuitable support structure. A piece of polypropylene 106 or othersuitable material may also be installed on the inside surface of thehinge joint 46 that faces the booth interior to function as a live gapseal and prevent powder from escaping the booth.

FIGS. 7, 8 and 9 illustrate an embodiment of the gun slot covermechanism 60. The gun slot cover mechanism 60 is used to open and closethe gun slots 61. When the gun slots are open, the spray guns can bemoved into and out of the spray booth. When the guns have been retractedfor a cleaning and/or color change operation, the gun slot cover 60 ispositioned so as to prevent powder from escaping through the gun slots.Due to the vertical length of the gun slots, a plurality of covers maybe used as required.

The gun slot cover mechanism 60 includes a flexible cover member 112that is mounted on a frame 114 using a ball and track arrangement 116. Acentral portion 118 of the cover member is attached to one end of apiston 120 that may be translated, for example, by a pneumatic cylinder122. A plate 124 supports two ball arms 126 which carry a guide ball 128thereon. The guide ball 128 slides within a channel 130 attached to thecover member 112. In order to open the gun slots, the piston 120 ispushed outward so as to displace the central portion 118 into the boothinterior. The cover member 112 includes two side portions 132 that bendinward as the balls 128 slide along the positionally fixed channels 130.This position is shown in phantom in FIG. 7. When the piston isretracted, the cover member 112 returns to the position illustrated inFIG. 7, which closes the gun slots and forms a smooth sealed gun slotpanel 42. Due to their length, as shown in FIG. 8, more than one drivemechanism may be used for each cover.

With reference to FIG. 10, because the spray guns are positioned on onlyone side of the spray booth, it may be necessary to double spray theparts. FIG. 10 illustrates an exemplary layout for a materialapplication system that uses two spray booths 200 and 202. The conveyor26 transports parts through both booths. Note that in this example thereare two after filter/blower systems 16, one for each cyclone system 15.As an alternative embodiment, a motor or other suitable drive mechanismmay be provided with the conveyor system so as to rotate the partsduring a coating operation. This would allow parts to be fully coatedwithin a single booth. Parts may also be manually repositioned forcomplete coating.

With reference to FIGS. 1, 11A and 11B, the spray guns 18 typicallyinclude one or more hoses and cables 305, including, for example,material feed hoses, air hoses and in the case of electrostatic guns,electrical cables. The material feed hose extends from the gun all theway to the feed center 21. The electrical cables may have to run asubstantial distance to an electrical control console (not shown) andthe air hoses will typically run a length to a supply manifold or othercompressed air source. Particularly in the case of powder feed hoses,for the guns located above normal human height, the hose runs can bequite lengthy. This is especially the case for guns near the top of atwenty-seven foot booth. These hose lengths can be quite heavy andrepresent a significant load for the gun movers and oscillators.

In accordance with an aspect of the invention, a strain reliefarrangement may be provided. This concept contemplates a mechanism thatlimits the load carried by the gun mover and oscillator while at thesame time allowing full range of gun movement during a powder coatingoperation.

Positioned behind the guns 18 are one or more hose cabinets 300 thatextend vertically about to the top of the spray booth 12. Mounted on thecabinets 300 are a plurality of strain relief devices 302. In theexemplary embodiment, there is a single strain relief device 302 foreach spray gun, however, one alternative would be to make the strainrelief devices of an appropriate size that each could accommodate morethan one gun.

Each strain relief device 302 includes a support cylinder 304 and a hoseclamp bar 306. A hose and, when used, electrical cables and air hoseextend from the associated spray gun, are provided a predetermined slacklength between the gun 18 and the cylinder 304 so that the gun mover andoscillator can freely move the guns as desired. The hoses/cables arepositioned over the top of the cylinder 304 and then the clamp bar 306is secured by any convenient means such as bolts 308. The clampingaction isolates the hoses and cable weight from the gun and gun moverexcept for the portion that extends from the gun 18 to the clamp bar306. In this manner, a fixed predetermined load can be maintained on thegun mover independent of the overall length of the hoses and cables.This also reduces force applied to the back end of the gun and stress onthe hoses and cables.

The hoses and cables run from the relief device 302 into the hosecabinet 300 and down to the floor area for further routing as needed.The cylinder 302 should be of sufficient diameter to prevent the hosesfrom collapsing under their own weight. Note that multiple cabinets maybe used as needed depending on the number and size of hoses and cablesbeing routed.

FIG. 12 is a simplified schematic of another feature of the invention.We have found that in some cases, eddy currents and other flow effectscan cause entrapment areas or pockets within the recovery duct interiorplenum 74. In an alternative embodiment, the interior plenum 350, whichit will be recalled is the duct through which powder entrained exhaustair enters the cyclone 15 via the recovery slot 62 and cyclone inlet 70,is provided with an offset or shifted slot opening 352, meaning that theslot is not centered on the central axis X of the plenum 350. Inaddition, the slot 352 opens to a tangential or tapered surface 354 thatjoins to the main plenum cylinder 356. This geometry produces aswirling, somewhat cyclonic action within the plenum 350 to reduce eddycurrents and entrapment areas or “dead spots.”

Even with the embodiment of FIG. 12, or with other configurations, theremay be surfaces 360 that are not fully cleaned by air flow within theduct work. FIG. 13 illustrates one solution to this possible anomaly. Anair blow off manifold 370 is mounted at one end to the ceiling or roof40 so that it travels with the roof during a cleaning operation. Theblow off manifold 370 may be realized, for example, in the form of ahollow composite extrusion 372 and may be provided with one or more airjets, slots or ports 374 that direct pressurized air 376 at the surfaces360 of concern.

Pressurized air may be supplied to the blow off manifold 370 from one ofthe accumulators 86 that are carried by the roof 40, or any othersuitable source. A pressure regulator 378 and solenoid valve 380 may beused to control flow of air to the manifold 370. The blow off manifoldmay be on continuously as the roof 40 travels down and up the booth 12during a cleaning operation, or may be pulsed.

FIGS. 14A and 14B illustrate some additional features that may be usedwith the roof 40 structure. In some cases when the roof 40 is fullyraised, such as during a spraying operation, it may be desired to pulsethe nozzles 50 before the conveyor slot cover 52 is closed. In order tomaintain stability of the roof 40 that is primarily supported on thecables 400, stabilizers 402 are provided that extend generallyvertically from the roof frame 404. These stabilizers 402 may be in theform of stanchions, bars or other suitably strong and rigid members thatare slideably received in a stabilizer channel 406 when the roof 40 israised. The stabilizer channels 406 are rigidly mounted to the overallframework 22 and thus hold the roof 40 stable even against the impulseforces of the nozzles 50.

The roof 40 structure also carries rollers 410. These rollers 410 bridgethe narrow gap between the roof 40 and the interior surfaces of thebooth doors as the roof 40 is raised and lowered, thereby stabilizingthe roof 40, keeping it centered and preventing extreme movement duringnozzle 50 pulses. The closed cover 52 (FIG. 3) also helps stabilize theroof 40 during cleaning operation. The rollers 410 may be provided withbrushes (not shown) to prevent powder from adhering to the rollers.Since the rollers 410 are positioned above the nozzles 50, the surfacesthey contact are clean so that powder is not pressed against the wallsurfaces.

It is intended that invention not be limited to the particularembodiment disclosed as the best mode contemplated for carrying out thisinvention, but that the invention will include all embodiments fallingwithin the scope of the appended claims.

1-17. (canceled)
 18. A powder spray booth comprising a wall structureand a gun slot formed in said wall, and a gun slot cover to selectivelyopen and close the gun slot; said gun slot cover comprising a flexiblesheet of material that flexes between a first position to open the gunslot and a second position to close the gun slot.
 19. The spray booth ofclaim 18 comprising an actuator to selectively bend the cover.
 20. Thespray booth of claim 19 wherein said actuator comprises a pneumaticcylinder and piston.
 21. The spray booth of claim 20 wherein said covercomprises polypropylene.
 22. The spray booth of claim 1 wherein thebooth has a vertical height that is at least about two times greaterthan its length. 23-27. (canceled)
 28. In a spray booth of the typehaving one or more gun slots, a gun slot cover having a first positionthat opens the gun slots and a second position that covers the gun slotsfor a cleaning operation.
 29. The booth of claim 28 wherein said gunslot cover is pneumatically driven. 30-44. (canceled)